Electric power rectifier cathode construction



March 1, 1932-. A. GAUDENZI 1,847,646

ELECTRIC POWER RECTIFIER CATHODE CONSTRUCTION Filed March 15, 1929 Fig. 2

15 i J 4 4 21 22 1 1a Inventor A rfhur. Gaudenzi B Attorney Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE ARTHUR GAUDENZI, OF IBADEN, SWITZERLAND, A SSIGNOR TO AKTIENGESELLSCHAFT BROWN BOVERI & CIE., OF BADEN, SWITZERLAND, A JOINT-STOCK COMPANY OF SWITZERLAND ELECTRIC POWER RECTIFIER CATHODE CONSTRUCTION Application filed March 15, 1929, Serial No. 347,270,:1116. in Germany March 15, 1928.

This invention relates to the improvements in the construction of metallic vapor rectifiers and, more particularly, to an improved cathode construction of the same.

The heating effect of the electric arc during the operation of metallic vapor rectifiers, especially when used in power installations and, therefore, in large sizes, produces excessive amounts of vapor thereby creating a vapor pressure which it is desirable to keep as low as possible for the purpose of preventing condensation of the metallic vapor on the anodes and on the walls of'the. rectifier chamber. Such condensation would result in the formation of a so-called cathode spot having a negative potential permitting a reverse flow of the current. The probability and the character of damage resulting from such backfires or reverse current are Well known in the art. Various means have been proposed to diminish the mass of metal-' lic vapor within the rectifier such as, cooling of the cathode, enclosing the anodes in separate chambers or supplying sleeves about the anodes, as well as many other means.

The excessive production of metallic vapor in electric current rectifiers is caused by movement of the arc over the surface of the oathode thereby uselesslyheating the entire surface of the cathode. The conditions to be met in preventing the formation of excessive vapor are; fixation of the arc to prevent movement thereof over the entire surface of the cathode, and cooling of the body of the cathode below the vaporization point so that the same may act as a condensing surface for the vaporized metal. 7

It is, therefore, among the objects of the present invention to provide a cathode for electric current rectifiers which will prevent the formation of excessive amounts of vapor therein.

Another object of the present invention is to provide a cathode structure for metallic vapor rectifiers in which the arc will be fixed or will be permitted to move only very slowly over the cathode surface.

A further object of the invention is to provide cooling means for the cathodes of metallic vapor rectifiers which will maintainthe cathode body at a temperature lower than the vaporization point.

Objects and advantages, other than those above set forth, will be apparent from the description and the drawings, in which Figure 1 is a partial vertical sectional view, showing one embodiment of the invention;

Fig. 2. is a similar partial sectional view of a modified form of an embodiment of the invention, and V Fig. 3 is a plan view taken on line AA, showing the structure of the arc fixing means.

Referring more particularly to the drawings by characters of reference, the reference numeral 5 indicates a portion of the bottom of a rectifier chamber and is formed, as is usual, in the shape of an inverted hollow truncated cone, which provides a circular aperture therethrough. The bottom may be made double walled to permit circulation of a cooling medium therethrough ormay be made as 'a single wall when cooling thereofis not required. i

A substantially cylindricalmember 6 of quartz or other equally diflicultly fusible, electrical insulating material is connected with the bottom 5 and, with a bottom closure plate 7 forms a container or well, the purpose of which'will appear hereinafter. The closure plate 7 is formed of copper or other material having a high coefficient of heat conductivity and is cut out, from the upper surface downwardly, to receive a cathode plate 8. 'Th'e'cathode plate Sis, preferably of good heat conducting material, formed as a complement to the cut out portion of closure 7 and is provided with perforations 10 connected by channels 11 cut into the under side of the plate.

The surface of plate 8 is covered or coated with a protective film 12 of some highly infusible material, such as tungsten, which extends partially into the perforations 10. Such filmmay be applied to the plate by any wellknown mechanical or electrolytic means.

An electrical'and heat insulating packing 13, preferably of asbestos, is arranged within cylinder 6 and is held in position by a sheath 15 of chromium orothe-r high melting point materialnot attacked by mercury. The

i. Although only two em sheath is inserted into a groove formed in plate 8 in contact with protective film 12 in such manner that it will be impossible for the electric arc to come into direct contact with plate 8, p The inner surface of cylinder 6 may also be coated with chromium or tungsten to increase the protection thereof against the action. of the arc. Sufiicient mercury is placed within the receptacle formed by sheath '15, plate Sand closure 7 to cover the protective film 12 on plate 8 to such depth that the same will be penetrated by the arc, during operation, in such manner that the arc will be fixed or attached totheifilin 12 and that the mercury meniscui in perforations 10 will always be in cont'a'ct'with film 12.

Any heaui 15,1 of the cathode structure is re- 'du'cedto a ldiv value by absorption of the heat in a: cooling medium flowing into a water-jacket formed by a chamber 16 arranged below-closure 7, through an inlet conduit 17 and escapin therefrom by way of an outlet conduit 18. The arcbeing fixed on film 12 vaporizes only that portion of the mercury immediately adjacent the point ofattachment while'the remainder of the cathode structure is cooled by conduction of heat through closure totlie cooling medium in water-jacket '1'6'. i

Q In a modified form of .the invention, shown in Fig closure 17 itself is hollowed out to forma chamber for the circulation of the cooling medium. Thecha mber is closed by an imperforate cathode p e 20 which is formed with grooves or cup-like depressions .Zplate 20 is covered with a protective sheath 22 conforming to the configuration thereof.

In this instance, the mercury fills the depressions 21.

[It will be apparent thatthe present invention provides a structure which will prevent excessive vaporization of mercury by dim nishing the movement oi the are over the su face of the cathode and by cooling the cathode structure iirsuch manner that conduction of heat'produced by the arc, to the entire cat-hode? is avoided.

H bodiments of the invent on have been illustrated and described, it

' will be'understood that various other embodiments are possible. and that various changes may be made w1thont departing from the spirit or the invention or the scope of the claims.

The invention claimed is: y 1.- In a cathode structure of an electric current rectifying device of the metall c vapor type having a bottom provided with an aperture there'through, an electrical insulating cylinder connected with said bottom; a closure member of heat conducting material connected with said CYllllClQl. a body of mercury retained within said insulating cylinderand said closure member, a heat conducting plate within the space enclosed by said cylinder 1,847,646 Qji 5 and said closure, exposed portions of said plate alternating with exposed surfaces of mercury, a sheath of diflicultly fusible material 'for protecting said plate from direct contact with an electric :arc, and means connected with-said closure for cooling the same.

2. In a cathode structure of an electric current rectifying device of the metallic vapor type having;abottomprovided with an aperture theretli'rough, an electrical insulating cylinder connected with said bottom, aclosure member of heat conducting material connected with said cylinder, a body of mercury retained within saidinsulatingcylinder and said closure member, means for protecting said cylinder from the-action of an electric are, means withinthe well formed by said cylinder and said closure for fixing the attachment of the electric are, a sheathing for protecting said means from direct contact with the arc, exposedportions ot'said sheathing alternating with exposedportions of mercury, and means connected with said closure for cooling the same;

3. Ina cathode structure of an electric cur-.

rent rectifying device of the metallic vapor type havmg'a bottom provided with an aperture theretlirough; an electrical insulating cylinder connected with saidfbottom, a c l-o- I sure member of heat conducting material 0011- L l nected with said cylinder, a heat conduct-- .ing plate within the space enclosed by said 

